The invention relates to a hub or pulley of sheet metal made by spin-roll forming, but more particularly, the invention relates to a hub with a blind bore and a method of shaping the hub.
Machined hubs are sometimes attached to webs and rims formed of sheet metal to make pulleys. A sheet metal web (or disc) and rim are attached to a machined hub by welding or brazing. A machined hub may provide complicated shapes such as a closed bore but it introduces the attendant problems of weight, expense, and a troublesome process of precisely attaching and aligning a web and rim portion to complete the pulley.
Hubs or pulleys of sheet metal may be shaped by press forming using a series of dies or spin-forming using mandrels and rollers or a combination thereof. For example, a pulley with an integral hub that is press formed is disclosed in U.S. Pat. No. 5,441,456 with a stepped bore in FIG. 5, and a bore with spline receiving grooves in FIG. 8. Belt receiving grooves are spin formed in the rim of the pulley. Another pulley with an integral hub is shown in U.S. Pat. No. 4,824,422. A troublesome area with the press forming and spin forming processes is they may introduce folded metal shapes that introduce high stress areas at folds that are subject to failure by cracking or fracturing from fatigue.
German Patent No. 4444526 discloses a method of shaping a hub by spin forming where a shaping roller is pressed against a side of a spinning annular disc of sheet metal that is supported at an opposite side with a head stock mandrel. The shaping roller is moved progressively radially inwardly against the side of the rotating disc which displaces a portion of metal while thinning part of the disc and forming a sidewall having a thickness that is less the original sheet metal thickness. An annular wave is formed as metal is displaced and which progressively, axially extends. A shaping roller presses the so annularly displaced metal against a mandrel while simultaneously forming a hub integral to the disc. The present invention relates to spin-forming of this type where a hub is integral with a web or disc and where a hub is formed of displaced metal from a side of the disc formed of sheet metal. A problem with such hubs is that complicated bore shapes (i.e. a blind bore) cannot be readily produced in comparison to machined hubs.